Specifying temperatures in MCNP

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Discussion Overview

The discussion centers on how to specify temperatures in the MCNP (Monte Carlo N-Particle Transport Code) cell cards, particularly in the context of a pressurized water reactor (PWR) example. Participants explore the necessary conversions and considerations for temperature settings in MCNP simulations.

Discussion Character

  • Technical explanation
  • Meta-discussion

Main Points Raised

  • One participant inquires about expressing temperature in the cell cards of MCNP, specifically for a fuel temperature of 500K.
  • Another participant explains that temperatures in cell cards should be expressed in MeV by multiplying the temperature in Kelvin by the Boltzmann constant (8.617e-11 MeV/K), providing an example for 600K.
  • It is noted that temperature considerations extend beyond cell cards to material cards, which require libraries generated at specific temperatures, referencing a document that includes this information.
  • Participants mention the importance of using the correct temperature S(alpha,beta) cards and provide a utility program "makxsf" for interpolating libraries at user-specified temperatures.
  • There is mention of ongoing development for "on-the-fly" temperature adjustments in future versions of MCNP, though the status is uncertain.
  • Several participants suggest changing the thread title to better reflect the topic of specifying temperatures in MCNP, indicating that the original title was misleading.

Areas of Agreement / Disagreement

Participants generally agree on the technical aspects of specifying temperatures in MCNP, but there is a lack of consensus on the appropriateness of the thread title, with multiple suggestions for a new title being made.

Contextual Notes

Participants reference specific documents and libraries related to temperature settings, indicating that there may be variations or updates in the resources available for MCNP users.

Aly_19f
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TL;DR
Temperature in MCNP
How do I express the temperature in the cell cards of the MCNP?, Say the temperature of the fuel is 500K, how do I write it as the following PWR example?
 

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In the cell cards, you specify the temperature in units of MeV by multiplying the temperature in Kelvin by the Boltzmann constant 8.617e-11 MeV/K. For example, 600K would be "tmp=5.17020E-08"

However, this is not the only place you need to worry about temperatures. In the material cards, you need to attach the library generated at the correct temperatures. A list of the library identifiers and temperatures used to be included in the "Appendix G" of the users manual, but it has now moved to a separate document. There may be a newer version, but I have report LA-UR-17-20709.
If you are using the ENDF/B-VII.1 cross sections, ".80c" is at 293.6 K, ".81c" is at 600 K, ".82c" is at 900 K, etc.

Finally, you also need to make sure you are using the correct temperature S(alpha,beta) cards. These can be found in Appendix G also.

If you need temperatures that do not line up with the library temperatures, there is a utility program "makxsf" that you can use to interpolate existing libraries and create libraries at user specified temperatures.

There is also development work to allow "on-the-fly" temperatures, but I am not sure what the status of this is. It will probably be released in a future version of MCNP.
 
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I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
 
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rpp said:
I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
@rpp -- Can you propose a new title? I think the edit window for the OP has expired, but the Mentors can change the title still...
 
berkeman said:
@rpp -- Can you propose a new title? I think the edit window for the OP has expired, but the Mentors can change the title still...
How about "Specifying temperatures in MCNP"?
 
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Done. Thanks!
 
rpp said:
How about "Specifying temperatures in MCNP"?
rpp said:
I also suggest that you change the name of the post to something that has to do with specifying temperatures in MCNP. Your question has nothing to do with supercritical water reactors.
I'm very thankful to you, and I apologize for the fatal mistake of the title but I couldn't edit it when I saw your reply two days ago.
 
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